textproduct: Rapid City

KEY MESSAGES

- Cool with showers likely through Friday.

- Mild and seasonal Saturday.

- Warmer conditions begin Sunday and last through next week.

DISCUSSION

(This Evening Through Wednesday) Issued at 1238 PM MDT Wed May 20 2026

Upper level analysis has a long wave trough extending through the Rockies into the Desert Southwest. At the surface, a lee trough extends through central Wyoming and a cold front extends from a surface low in southern Saskatchewan into the Pacific Northwest. Radar has a few showers across southwestern and south-central South Dakota.

For this afternoon and tonight, the lee trough will move into the forecast area and energy from the approaching trough will combine with increasing low-level moisture to support a few isolated showers and thunderstorms. NBM washed out these features, so decided to broad-brush 20 pops over the northern/central Black Hills. Showers will quickly dissipate after sunset with the loss of diurnal heating.

There will be a break in the precipitation overnight and into Thursday morning. Chances for showers will return by midday Thursday as the upper trough approaches the area. Diurnal heating combined with sufficient moisture will support convection initiating along the trough and the Black Hills. Showers and isolated thunderstorms will continue into Friday as the main trof axis moves through. NBM probabilities for precip >= 0.25" has a wide swath of 60 to 80 percent over most of western SD, excluding far northwestern SD and the plains of northeastern Wyoming. Based off the current track of this system, highest QPF amounts are expected in the Black Hills, southwestern, and south-central South Dakota.

The upper ridge slowly rebuilds over the weekend, allowing for a return of warm temperatures. Additionally, strong thunderstorms may be possible Tuesday and Wednesday next week.

AVIATION

(For the 18Z TAFS Through 18Z Thursday) Issued At 1118 AM MDT Wed May 20 2026

VFR conditions expected through most the forecast period. Isolated showers and thunderstorms are possible across portions of western SD into south-central SD where transient MVFR conditions are possible. Gusty, erratic winds may be present near thunderstorms that develop.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.